It is important to remove the bark in withes collection, especially if they are to be stored for any great length of time. The soft wood underneath the bark is quite pliable, and can remain flexible if processed correctly. For withes to maintain permanent flexibility, they are heated over a fire, and then the lateral bonds between the fibres are broken by twisting the withes (and keeping them twisted). Another method to ensure flexibility is to twist the withes while they are still on the tree, and to cut off the resulting product with a knife.